1. Field of the Invention
This invention relates to a heavy duty pneumatic tire for use in truck, bus, construction vehicle and the like, and more particularly to a heavy duty pneumatic tire capable of improving wear resistance and effectively controlling heat generation in a tread portion (particularly a central land portion) during the running of the tire under loading to prevent separation failure through heat by using rubber having specified properties in a tread rubber and rationalizing lug grooves and shape of the central land portion.
2. Description of Related Art
In the conventional heavy duty pneumatic tire for use in truck, bus, construction vehicle and the like having so-called lug pattern formed by arranging a plurality of lug grooves at given intervals, it is common to use means for increasing a tread volume, means for increasing a tread gauge (increase of groove depth), means for reducing a negative ratio, means for enhancing stiffness of land portion (e.g. decreasing pitch number of lug grooves to increase a ratio of land portion), and the like for improving the wear resistance of the tire.
When the wear resistance is improved by using the above means, however, it particularly tends to bring about the degradation of heat build-up in the tread portion during the running of the tire under loading. The degradation of heat build-up causes the occurrence of troubles such as separation failure of tread portion through heat and the like.
Lately, there is a remarkable tendency of degrading the beat build-up in the tread portion with the advance of size-enlarging, flattening and heavy-loading of the tire accompanied with the increase of the size in the construction vehicle or the like.
It is, therefore, an object of the invention to provide a heavy duty pneumatic tire capable of improving wear resistance and effectively controlling heat generation in a tread portion (particularly a central land portion) during the running of the tire under loading to prevent separation failure through heat by using rubber having specified properties in a tread rubber and rationalizing lug grooves and shape of the central land portion.
According to the invention, there is the provision of in a heavy duty pneumatic tire comprising a tread portion, a plurality of lug grooves formed in the tread portion and extending from each end of the tread portion toward an equator of the tire, and a central land portion continuously extending between two circumferential lines each formed by connecting terminal positions of these lug grooves substantially in a circumferential direction of the tire, the improvement wherein a tread rubber constituting the tread portion has a loss tangent at room temperature of 0.04xcx9c0.40, and a negative ratio at a region corresponding to at least 50% of a tread width around the equator is 10xcx9c30%, and a maximum value of a groove depth of the lug groove located at a zone corresponding to at least 80% of the tread width around the equator is not less than 60 mm, and a circumferential shallow groove extending along the circumferential direction of the tire is formed in the central land portion.
In a preferable embodiment of the invention, the circumferential shallow groove has a groove depth corresponding to not more than 25% of the maximum value of the groove depth of the lug groove and a groove width corresponding to 30xcx9c80% of a vertical distance between the two circumferential lines.
In another preferable embodiment of the invention, the tire has an aspect ratio of not more than 90%.
In the other preferable embodiment of the invention, a coefficient in correspondence with a maximum speed in the Load/Inflation Pressure Table for construction vehicle tire defined in TRA is not less than 1.4.
In a still further preferable embodiment of the invention, the tire is a tire for wheeled crane or mobile crane.